Field of the Invention
The present invention relates to an imaging apparatus and an imaging system.
Description of the Related Art
An imaging apparatus is known in which an analog-to-digital (A/D) conversion circuit configured to convert an analog signal into a digital signal through comparison between an analog signal read out from a pixel and a reference signal (ramp signal) is arranged correspondingly to each pixel column. In such an imaging apparatus, a technology is also known in which the value of the digital signal after the A/D conversion is made variable through changing the slope of the ramp signal.
In Japanese Patent Application Laid-Open No. 2009-130828, there is disclosed a technology configured to correct a difference in slope among ramp signals due to wiring lengths of ramp signal lines through adjustment of a gain of a pixel signal or a ramp signal to suppress shading that appears in an output image.
In an imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2009-130828, due to process variations in resistance values and capacitance values in amplifier circuits, there is a limit to the extent of improvement of precision of the gain adjustment. Further, in Japanese Patent Application Laid-Open No. 2009-130828, there is no disclosure of a correction of a difference in slope when a technology in which the slope of a ramp signal is variable is used.
Further, when a plurality of ramp signals having different slopes are used to perform A/D conversion, a configuration is conceivable in which the slope of a ramp signal is changed by capacitance division. However, in this configuration, the slopes of ramp signals supplied to the respective column circuits may vary due to process variations of the capacitance value or the like. This results in variations in the signal level after the A/D conversion among columns, which may be a cause of noise, e.g., vertical stripes in an output image.